1. Field of the Invention
The present invention pertains to a system and method for determining the concentration of a fluid such as hydrogen sulfide in a liquid hydrocarbon by measuring the indicated incremental gas phase concentration after adding a known quantity of the fluid to be measured to a liquid flowstream which is in equilibrium with a vapor flowstream being measured.
2. Background
The concentration of one fluid in vapor form which is in equilibrium with a liquid such as a liquid hydrocarbon depends on an equilibrium constant which is a function of the temperature and the composition of the liquid. For example, in determining the concentration of hydrogen sulfide in a hydrocarbon flowstream there are various types of measuring devices which measure the concentration of the hydrogen sulfide in a vapor flowstream which is in equilibrium with a quantity of liquid hydrocarbon. One type of device which is known as an MOS detector produces an electrical signal which is determined by the competitive adsorption of oxygen and hydrogen sulfide when exposed to a semiconductor. Accordingly, the signal response of this device depends on the oxygen concentration as well as the hydrogen sulfide concentration in the vapor. Other types of hydrogen sulfide concentration detectors are known, such as a type which produces a chemical change in a tape which is exposed to the vapor stream and a photoelectric device monitors the change in color of the portion of the tape which has been exposed to the vapor stream. Although this type of detector does not require the presence of oxygen in the vapor stream, it is mechanically complicated.
It has been determined that there is a need for a mechanically uncomplicated and reliable system and method for determining the concentration of a fluid in a continuous stream of another fluid which does not rely on the competitive concentrations of different substances in the fluid flowstream and which can accurately determine the concentration of a fluid in a liquid flowstream based on the indicated concentration of the fluid in a vapor flowstream which is in equilibrium with the liquid flowstream. It is to this end that the present invention has been developed.